First of all read documentation for boto3 dynamo, it's pretty simple:
http://boto3.readthedocs.io/en/latest/reference/services/dynamodb.html
If you want to provide access keys while connecting to dynamo, you can do the following:
client = boto3.client('dynamodb',aws_access_key_id='yyyy', aws_secret_access_key='xxxx', region_name='***')
But, remember, it is against best practices from security perspective to store such keys within the code.
For best security efforts use IAM roles.
boto3 driver will automatically consume IAM role if it is attached to the instance.
Link to the docs: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/iam-roles-for-amazon-ec2.html
Also, if IAM roles is to complicated, you can install and aws-cli and run aws configure on your server, and boto3 will use the key from here (less secure than a previous approach).
After implementing one of the options, you can connect to DynamoDB without the keys from code:
client = boto3.client('dynamodb', region_name='***')